10 Answers
10

Personal - some people are exceptionally private, especially in this day and age, and would like to remain so in their personal lives.

Professional - much like other artists, authors can be tied to a specific style of writing or genre. Existing fans can be upset if an author experiments in another genre, and new fans can't be picked up if they automatically assume everything the author writes is not something they'd like to read.

@John: thanks, I thought that sentence had run away with me. :)
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Zayne S HalsallJun 18 '11 at 17:15

1

An additional point 3: Legal. Some may do it to avoid legal repercussions, which is different to "personal".
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Craig SeftonJun 25 '11 at 13:22

@ZayneSHalsall is it recommended to use pseudonyms?
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gaussblurincJan 14 '13 at 8:56

That would be subjective opinion on my part - directly against the SE Q&A format. But in the interest of giving you something to think about, I fully intend using at least one pseudonym (personal reasons) when I finally get something ready to publish, perhaps more dependent on publisher direction/advice (professional reasons).
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Zayne S HalsallJan 14 '13 at 17:47

Sometimes pen names are used to fit with an imaginary "true story". A great example is The Princess Bride, in which the real author (William Goldman) pretends it's a "true story" written by someone of the era (S. Morgenstern).

Still, that falls under Marketing I guess.

Another reason is that an author may want to be shelved with other authors of their genre, especially highly successful authors. For instance, if you were a fantasy author it might seem attractive to have your novel sitting next to Tolkien's great works. Thus, anyone looking for Tolkien may stumble across yours.

Women writers used to do it because only men authors were taken seriously. Sometimes people don't want the fame from their writing they just want to do it for the art. The pen name allows them peace from the hype of their book. Sometimes people are afraid of critics and feel better if its not actually their name being bashed it makes it feel less personal.

To expound on your first sentence, Charlotte, Anne, and Emily Brontë used masculine pen names because they thought they wouldn't be taken seriously as women, as described here.
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ThunderforgeJun 25 '13 at 6:59

Zane hit the main ones: desire for personal privacy the other primary reason I know is marketing - same as actors, some authors will adopt snazzier-sounding names to sound good on the bookshelf.

Beyond that, you've got a lot of exceptional cases - Joe Hill is a pen name to avoid the otherwise-painfully-blatant connection to his father; Alice Bradley Sheldon probably falls under "privacy" but in a very extreme manner, etc. etc.

One unusual reason I haven't seen touched on: Some people do it to access a side of them that they want to express, creating a kind of virtual "person" with different attributes. Some people call it their "muse" and other pet names.

It's a way of allowing themselves to overcome some mental barrier by pretending to be someone else, with special "powers", like a kind of super writer with confidence they might not normally possess.

Of the Brontë sisters' motivation to use pseudonyms Wikipedia has to say:

In 1846, the sisters' poems were published in one volume as Poems by
Currer, Ellis, and Acton Bell. The Brontë sisters had adopted
pseudonyms for publication: Charlotte was Currer Bell, Emily was Ellis
Bell and Anne was Acton Bell. Charlotte wrote in the "Biographical
Notice of Ellis and Acton Bell" that their "ambiguous choice" was
"dictated by a sort of conscientious scruple at assuming Christian
names positively masculine, while we did not like to declare ourselves
women, because... we had a vague impression that authoresses are
liable to be looked on with prejudice[.]"